1. Field of the Invention
The present invention relates to rotation or spin measurements for rotating missiles. More particularly, this invention pertains to apparatus for rotation or spin measurement for stabilization of rotating missiles.
2. Description of the Prior Art
The ability to measure and process high roll spin rates of rotating missiles (e.g., 5000 to 10,000xc2x0/s) is a fundamental requirement of a flight attitude stabilization device for maintaining specific roll, pitch and azimuth angles with respect to an initial position.
The options for solving this fundamental problem are briefly outlined below:
(a) spin-stabilized two-axis integrating gyro systems (i.e., cold gas or powder gyro arrangements);
(b) optical gyro systems having high spin rate capacity and scale factor stability, (e.g., ring laser or fiber optic gyros);
(c) vibration gyroscopes based on the Coriolis principle in which symmetrical oscillator structures oscillate within a plane subject to as little damping as possible and provide high scale factor of accuracy.
The first two approaches (xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d) satisfy the technical requirements while incurring excessive unit costs. In the traditional, mechanical integrating solution (proposal a), the gyro systems are constructed from mechanical parts which, from the beginning, offer economies when relatively large quantities are employed. This solution suffers the substantial disadvantage that functional tests prior to missile launch are possible only to a limited extent. In practice, such tests can only be carried out on a sample test basis because it is too risky due to particles to renew or replace the gas or powder reservoir. This is possible only at a considerable cost and this solution suffers under limited reliability because of the testability restrictions.
The bias of optical gyro systems according to proposal b can be readily checked, even after long storage times. High scale factor accuracy is required to measure high spin rates and can only be checked with difficulty. Expensive tests on rotating tables are unacceptable after the missile has been stored for a long period of time. Proposals exist for monitoring the scale factors of ring lasers and fiber optic gyros within systems, with accuracy requirements of, e.g., 0.02%, over storage times of up to 20 years. However, unit costs for optical gyros become unacceptably high, even when the fact that optical components and assemblies are becoming ever cheaper due to newer production methods is taken into account.
Initially, a vibration gyroscope according to proposal xe2x80x9ccxe2x80x9d would appear to offer a highly promising solution to the problem. Induced vibration in an ideal resonator with high Q-factor retains its inertial orientation even at high roll rates. Thus, in theory, an ideal spin-rate integrating gyroscope system is possible. However, known resonators cannot, in fact, be produced with such ideal characteristics. Tuning fork oscillators, as well as ring or circular oscillator systems, for example, have a number of oscillation modes and natural frequencies that must be matched to one another. Thus, ring oscillator configurations, for example, do not maintain their inertial orientations due to the Bryan factor. Theoretically, an output oscillation angle of about 60% with respect to the input angle is obtained. However, the 60% discrepancy depends upon the actual natural modes and respective mechanical coupling. Should they change, due to external vibration or shocks during storage, the scale factor then changes. As a result the 0.02% accuracy requirement cannot be satisfied over a relatively long storage period.
In the case of double tuning fork oscillators, the Bryan factor is virtually 100%. Discrepancies of about 1.3% must be taken into account, so that the required scale factor stability of 0.02% is virtually impossible to achieve after storage for up to 20 years. Furthermore, checking involves major practical difficulties.
A further problem of both vibration gyroscope concepts results from unavoidable damping. In practice, to insure operation as a spin rate integrating gyroscope, damping must be electronically overcome (at least for the two modes employed). Constant excitation is required for the initial vibration mode. Damping for the other oscillation mode must be overcome, for example, by electronic torquers, without forcing such oscillation mode absent Coriolis forces. If the damping cannot be correctly overcome, considerable errors will occur in integrating gyroscopes, perhaps sufficient for the two oscillation modes to become unstable.
To compensate for temperature-dependent gas damping, vibration gyroscopes would have to be operated in a vacuum, particularly for miniaturized designs. It is, however, difficult and expensive to maintain a stable small volume vacuum over long storage times (up to 20 years).
It is therefore an object of the present invention to provide a spin rate measurement device for stabilizing the track attitude of rotating missiles.
It is a further object of this invention to achieve the above object while obtaining high bias and scale factor stability in a missile that has been stored for a long time.
It is yet another object of the present invention to achieve the foregoing objects with a device having good testability and low unit costs.
The present invention achieves the above and other objects by providing a spin rate measurement device for rotating missiles. Such device includes at least one micromechanical spin rate sensor. The sensor is mounted on a platform. One axis of the platform can be driven in a controlled manner by means of a servo loop for rotation decoupling of the spin rate sensor.
The preceding and other features of the invention will become further apparent from the detailed description that follows. Such description is accompanied by a set of drawing figures. Numerals of the drawing figures, corresponding to those of the written description, point to the features of the invention with like numerals referring to like features throughout both the written text and the drawing figures.